1. Field of the Invention
The present invention relates to an image processing apparatus, an image processing method, and a program.
2. Description of the Related Art
With the widespread use of information processing devices in recent years, it has been more customary than ever before for people to carry small-size information terminals that store highly confidential information. Using biological characteristics of the user of an information terminal as an authentication technique to protect such confidential information is one of the best approaches to prevent others from “impersonating” the user. Of various biological authentication techniques, fingerprint authentication in particular is promising in that it allows information terminals to be easily reduced in size, the cost required to construct fingerprint authentication devices is relatively low, and fingerprints differ from person to person and do not change with time.
Many devices for reading fingerprints traditionally comprise a two-dimensional sensor, i.e., a planar sensor (see FIG. 1A of the accompanying drawings). However, the recent tendency toward small-size information terminals has drawn much attention to a one-dimensional sensor, i.e., a line sensor (see FIG. 1B of the accompanying drawing).
The line sensor is a device that has been developed for the purposes of achieving smaller sizes and low prices. A fingerprint reading sensor as an example of line sensor is a device for generating image data of a fingerprint from a number of sectional image (slice) data that are successively acquired when a finger is moved across the fingerprint reading sensor (such an action is hereinafter referred to as “sweeping”).
One conventional line sensor that has been proposed as a fingerprint reading sensor is a fingerprint identifying device having a frame input unit, an optimum position calculator, a template image memory, a partial synthetic image memory, an image synthesizer, a checking feature extractor, a template checking feature memory, and a fingerprint feature checking unit (see, for example, JP-A-2002-42136). For reconstructing an overall image from a series of partial images entered from the frame entering unit, the optimum position calculator checks a partial image against a fingerprint image (template image) of the user that is stored in the template image memory to determine a position where the similarity is the highest, and the image synthesizer joins the partial image to a partial synthetic image that is stored in the partial synthetic image memory. The above process is carried out for each of partial images that are produced, thus generating a synthesized image. Then, the checking feature extractor extracts features from the synthesized image, and the fingerprint feature checking unit checks the extracted features against features in the template image that are stored in the template checking feature memory. The fingerprint identifying device is capable of confirming the user quickly and accurately using a group of partial images of the fingerprint that are produced by the relative movement between a sensor having a small area and the finger.
However, when fingerprint images are generated with the conventional line sensor, the user is likely to sweep the finger differently across the line sensor for various reasons. For example, the user may move the finger in a direction that is opposite to the direction which the user is expected to follow in sweeping the finger across line sensor (see FIG. 2A of the accompanying drawings), or the user may sweep the finger along a curved path across the line sensor because of the way the line sensor is installed or the motion of finger joints (see FIG. 2B of the accompanying drawings). If the finger does not sweep the line sensor as expected, then it is difficult for the line sensor to produce accurate fingerprint images.
The above problem occurs with not only fingerprint reading sensors, but also other line sensors such as sensors for use in scanners.